1. Technical Field
This invention relates to the technology of movable load-supporting platforms, and more particularly to pallet conveying devices having roller elements.
2. Discussion of the Prior Art
Low friction load-supporting platforms facilitate the movement of goods within a manufacturing facility. Predominantly, the platforms have load-bearing conveyors with a large number of ball or roller elements projecting upwardly above the supporting members to movably support the goods or pallet containing the goods; such conveyors may have the roller elements powered to promote continuous movement of the goods. Such conveyors suffer from two inherent limitations: unidirectionality and inability to asynchronously stop and go at various stations along the conveyor without affecting the stream of goods.
With respect to alleviating the lack of independent stop and go, the prior art has attempted to use guided vehicles, linear induction motors, and zone control conveyors, all of which rely on complex and expensive electromechanical drives and control systems and thus share a history of extraordinarily high costs and/or inadequate reliability.
With respect to alleviating unidirectionality, the prior art has attempted to use rotary trays or raiseable diverter rails to change direction 90.degree. at interruptions in or at the end of a conveyor line (see U.S. Pat. Nos. 3,011,665 and 4,798,275). This is disadvantageous because it limits bidirectionality to only specific turnoff stations and requires separately complex mechanisms.
More recent approaches comprise the use of inflatable bladders to lift a transverse roller deck into contact with a load pallet, and subsequently raise the pallet above longitudinally directed rollers, allowing the load to be moved transversely to the original direction of motion. This may be accomplished directly by manually moving the load pallet on such transverse rollers or indirectly by powering the transverse rollers such as disclosed in U.S. Pat. No. 4,747,477. It also may be accomplished by causing bladders to raise and push upwardly on the transverse carriage in a manner to cause the long flange of the carriage to engage part of the support and tilt encouraging gravity to move the goods (see U.S. Pat. No. 4,627,526). The problem associated with the attempt to use inflatable bladders is their limitation to dedicated directions and inability to achieve asynchronous stop and go.
What is needed is a flexible conveying device that provides for omnidirectional movement capability along with stop and go characteristics in a modularized system that is both low in cost and extremely durable.